Cyclin-dependent kinase inhibitor p27(Kip1) expression in thyroid cells obtained by fine-needle aspiration biopsy: A preliminary report

Recent studies on paraffin-embedded tissue have shown that the cyclin-depen dent kinase inhibitor p27(Kip1) is expressed in normal thyroid cells, where as it is downregulated in neoplastic cells. This prospective study was unde rtaken to assess whether p27(Kip1) staining may also be applied to fine-nee dle aspiration biopsy (FNAB) samples of the thyroid. We present here our pr eliminary results on 100 FNABs examined for p27(Kip1) expression. p27(Kip1) expression was assessed by immunocytochemistry; the technique was optimize d on smears prepared from a normal thyreocyte cell line (TL5), which conspi cuously expresses p27(Kip1), and then applied to FNAB samples prospectively collected from 80 cases of nodular goiter and 20 cases of thyroid neoplasm s (10 papillary carcinomas and 10 follicular neoplasms). The TL5 cell cultu re smears showed that methanol fixation, followed by heat-induced antigen r etrieval, is the most suitable technique for p27(Kip1) Staining on cytologi cal samples. The FNAB smears similarly treated showed high p27(Kip1) expres sion (75%) in goiter and a significantly lower expression (35%) in neoplasm s (P < 0.0001). Our preliminary results show that: 1) p27(Kip1) protein exp ression can be reliably assessed on cytological samples; and 2) p27(Kip1) s tains nonneoplastic and neoplastic samples in a different fashion, and thus is a useful tool in thyroid cytology. Diagn. Cytopathol. 2000,23:77-81. (C ) 2000 Wiley-Liss, Inc.